The central aim of this project is to determine the relationships among articulation-based phonetic aspects of child speech, the acquisition of language-specific phonological features, and the use of phonemic contrast in learning to talk. These relationships will be investigated through cross-sectional and longitudinal studies of infants and toddlers acquiring American English, and cross-sectional comparative investigations of English and Swedish-learning subjects, using perceptual (phonetic transcriptions) and acoustic (instrumental) analyses. The data for the crosslinguistic studies have already been collected and analyses are currently underway. The crosslinguistic studies will trace the development of particular consonant and vowel phones that occur in both English and Swedish in order to determine when and how they diverge from one another and become closer to the adult forms of the ambient language. It is hypothesized that in the prelinguistic stages, infants from both language groups will produce consonants that resemble the "unmarked" or "default" forms most common to languages of the world. The within-language studies are based exclusively on English and focus on phonetic and phonological comparisons of coronal and dorsal stop consonants ([t,d,k,g]) and the high front vowels [1] and [I]. Data for these studies are derived from cross-sectional samples gathered at 3-month intervals from subjects aged 9-33 months. The goal of these studies is to trace the phonetic and phonological development of the consonants and vowels of interest with particular attention to (a) articulatory changes that occur with age; (b) the influence of phonemic context on production of a target phoneme (e.g., consonant-vowel interactions; the effects of stress in word productions; the role of contrastivity in the developing system). The key personnel of this project combine expertise in child phonology, acoustic phonetics and phonetic transcription. The research design provides a multi-dimensional perspective including studies within and across languages of prelinguistic and early linguistic periods, data from cross-sectional and longitudinal subjects, and acoustic and perceptual analyses. The findings from the series of proposed studies will lead to a more complete understanding of the process of phonological acquisition int he young child and will serve as basis for investigations of children with phonological disorders.